Metal fastener with embedded RFID tag and method of production

ABSTRACT

The present disclosure is generally directed to an RFID tag for use with a metal fastener where the fastener operates as the antenna of the RFID tag. The RFID tag includes a microchip for storing data. The chip is electrically coupled to the metal fastener in order to receive and transmit the RF signal, the metal fastener thereby operating as the antenna for the RFID tag.

RELATED APPLICATIONS

This patent is a CONTINUATION of U.S. patent application Ser. No.16/859,873, filed Apr. 27, 2020, which is a CONTINUATION of U.S. patentapplication Ser. No. 16/246,317 filed Jan. 11, 2019, which claimspriority to U.S. provisional application 62/616,279 filed Jan. 11, 2018,and U.S. provisional application 62/774,132, filed Nov. 30, 2018. Allreferences cited in this section are incorporated here by reference intheir entirety.

TECHNICAL FIELD

This invention relates generally to a metal fastener, and morespecifically to a metal fastener having a radio frequency identification(RFID) tag embedded in the head or body of the fastener, where the metalfastener operates as the antenna for the RFID tag.

BACKGROUND

Radio frequency identification systems (RFID) are a form of wirelesscommunication that utilizes radio waves to identify and track objects.Each tag carries a unique identification number; which is programmed atthe time of manufacturing to ensure the object carries a distinctiveidentity and description. Conventional RFID systems, such as the oneshown in FIG. 1 , typically include a reader (or an interrogator) and atag (or transponder). The tag includes a microchip that stores data andan attached antenna. FIG. 2 illustrates a prior art RFID tag with asimple dipole antenna structure 3. The tag 1 includes a chip 2 coupledto the dipole antenna structure 3, which includes of a pair of antennaelements 4 and 5 supported on a substrate 6.

RFID tags can be attached to an object, i.e. substrate, and can store ortransmit information concerning the object, such as a unique identifyingnumber, object status such as opened or unopened, location, and thelike. There are two different methods of communicating with an RFIDtag—near-field and far-field, with the main difference between the twomethods being the reading distance. Near-field communication isconventionally defined as having distances of less than 1.5 m, whilefar-field communication is more than 1.5 m. Additionally, RFID tags maybe passive, active, or semi-active.

Near-field communication (NFC) transmits data either through inductivecoupling between the reader and the tag, or through capacitive coupling,with inductive coupling being more popular in use. Inductive couplinginvolves the use of a magnetic field to energize the RFID tag. Amagnetic field is created in the near-field region that allows the RFIDreader's antenna to energize the RFID tag, which then responds bycreating a disturbance in the magnetic field that the reader will thendetect. Capacitive coupling is less common than inductive coupling inNFC and utilizes a quasi-static electric field between the readerantenna and the tag antenna.

Far-field communication (FFC) involves sending and receivingelectromagnetic (EM) waves, typically through the use of capacitivecoupling (or propagation coupling). The reader transmits a signal thatis then reflected off the tag and returned to the reader. By modulatingthe load on the tag, data can be encoded in the modulating reflectedsignal. Compared to NFC, the reading distance for FFC is typically morethan 1.5 m.

Passive tags have no power source and instead draw power from the fieldcreated by the reader and use the energy from the field to power themicrochip's circuits. With passive RFID, the RFID tag is irradiated withradio frequency waves from the RFID reader. The RFID tag uses the energyfrom the radio frequency waves to emit an RFID signal, containing theRFID tag identification location or other data, back to the RFID reader.The RFID reader then receives the RFID tag information and software canbe used to interpret the information on the tag, such as calculate atag's location.

Active tags have a power source and broadcast their signal at setintervals rather than relying upon signals from the reader. Active RFIDtags have an independent onboard power source, such as a battery, or areconnectable to one. Active RFID tags can transmit the Radio Frequencysignal autonomously, at a selected time or at programmed triggers, forexample, from a temperature sensor. The power source on active RFID tagsalso gives them a longer range than passive RFID tags.

Semi-active tags, like active tags, also have a power source, but differin that they wait for a reader to communication with them, similar topassive tags. Also similar to passive tags, these tags utilize the powerfrom the reader's transmission to communicate back to the reader.Compared to passive tags, semi-active tags contain more complexelectronics and are thus more expensive, but can be read from a fartherdistance, faster and through opaque materials.

While there are different types of RFID systems, in most systems thereader sends out electromagnetic waves, which the tag is designed toreceive. Depending on the structure, the RFID reader can identify itemsthat are anywhere from a few centimeters to several meters away. Thesize of the RFID tag's internal antenna is one indicator of the tag'srange. Generally, small RFID tags contain small antennas and shorterread ranges, while large RFID tags that contain larger antennas havelonger read ranges. Additionally, RFID antennas can be stronglyinfluenced by their surrounding environment. Water can absorb andreflect RF energy and therefore may decrease an RFID system'sperformance, including read ranges and read rates.

RFID technology has been used in various capacities. For example, RFIDtechnology may be used for identification of products. The microchip inthe RFID tag may contain information that aids in identification of theitem to which the RFID tag is attached. Unlike bar codes, which requiredirect line-of-sight for access (i.e., the bar code needs to be visiblein order to be scanned), RFID tags can be read by the RFID readerwithout the need for direct line-of-sight. RFID tags also have greatercapabilities than bar codes because much more information can be storedon the RFID tag than can be printed on a bar code.

SUMMARY

In industries such as the aerospace industry, the tracking of parts canbe particularly useful as part of quality-control records, and forpurposes of recalls and replacement of aging parts. However, currentlyparts are often tracked by part numbers that are printed on the part,and which are subject to wear, may be particularly small, all of whichcan create a challenge to accurately and reliably track the parts.

While RFID tags find use with a variety of products and industries, thetag-antenna typically must be placed more than 0.05 wavelengths awayfrom a metal substrate. In applications where an RFID tag is to beattached to a metal substrate, the dipole antenna impedance oftenbecomes too small, and matching becomes problematic. Thus, use of RFIDtags with goods having metal substrates imposes unique challenges asopposed to other goods, particularly when the parts made from thesubstrate are small in size, as is the case with metal fasteners, whichmay have a head diameter in the range of approximately 3/16″-½″ andwhich may have a shaft diameter in the range of approximately ⅛″ to ¼″(shaft diameter).

An RFID tag for use with a metal fastener is disclosed herein where thefastener operates as the antenna of the RFID tag. The RFID tag includesa microchip for storing data the chip being embedded or otherwisesecured into the metal fastener. The chip is electrically coupled to themetal fastener in order to receive and transmit the RF signal, the metalfastener thereby operating as the antenna for the RFID tag.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of at least one embodiment are discussed below withreference to the accompanying figures, which are not necessarily drawnto scale, emphasis instead being placed upon illustrating the principlesdisclosed herein. The figures are included to provide an illustrationand a further understanding of the various aspects and embodiments, andare incorporated in and constitute a part of this specification, but arenot intended as a definition of the limits of any particular embodiment.The figures, together with the remainder of the specification, serveonly to explain principles and operations of the described and claimedaspects and embodiments, but are not to be construed as limitingembodiments. In the figures, each identical or nearly identicalcomponent that is illustrated in various figures is represented by alike numeral. For purposes of clarity, not every component may belabeled in every figure.

FIG. 1 is a schematic view of a prior art RFID system;

FIG. 2 is a perspective view of a prior art RFID tag; and

FIG. 3A is a top view of a fastener including an RFID tag in the head(RFID fastener), in accordance with a first embodiment;

FIG. 3B is a side, perspective view of the RFID fastener of FIG. 3A,illustrating the RFID tag in both the head and the shaft of thefastener;

FIG. 3C is a bottom view of the RFID fastener of FIG. 3A including anRFID tag in the shaft;

FIG. 4 is a side perspective view of a second embodiment of a fastenerin communicative connection with an RFID tag, in accordance with thepresent disclosure;

FIG. 5 is a schematic view of a circuit of an RFID tag, showing anantenna, network, and RFID chip, in accordance with an exemplaryembodiment for use with a fastener according to the present disclosure;

FIG. 6 illustrates exemplary code for theoretical reflection coefficientdata calculated using the MATLAB Antenna Toolbox for comparison with anRFID fastener in accordance with the present disclosure;

FIG. 7 is a graphical representation of the reflection coefficient dataof an RFID fastener in accordance with the an exemplary embodiment;

FIG. 8 is a schematic view of an exemplary circuit for an RFID faster inaccordance with the present disclosure for use with a T-matchingnetwork;

FIG. 9 is a schematic view of an exemplary printed circuit boardfootprint for an RFID fastener in accordance with the present disclosurefor use with a T-matching network;

FIG. 10 is a graphical representation of the relationship between loopdiameter and maximum distance of minimum read communication, inaccordance with the present disclosure, specifications of which areprovided in FIG. 12 ; and

FIG. 11 shows the specification for the ALR-H450 RFID reader by Alien;

FIG. 12 shows the specification for the Higgs 4 chip by Alien;

FIGS. 13A and B are graphical representations of reflection coefficientdata obtained using a VNA and a theoretical model according to thepresent disclosure, respectively; and

FIG. 14 is pictorial representative of one example of a workingprototype in accordance with the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The examples of the apparatus discussed herein are not limited inapplication to the details of construction and the arrangement ofcomponents set forth in the following description or illustrated in theaccompanying drawings. It will be understood to one of skill in the artthat the apparatus is capable of implementation in other embodiments andof being practiced or carried out in various ways. Examples of specificembodiments are provided herein for illustrative purposes only and arenot intended to be limiting. Also, the phraseology and terminology usedherein is for the purpose of description and should not be regarded aslimiting. Any references to examples, embodiments, components, elementsor acts of the apparatus herein referred to in the singular may alsoembrace embodiments including a plurality, and any references in pluralto any embodiment, component, element or act herein may also embraceembodiments including only a singularity (or unitary structure).References in the singular or plural form are not intended to limit thepresently disclosed apparatus, its components, acts, or elements. Theuse herein of “including,” “comprising,” “having,” “containing,”“involving,” and variations thereof is meant to encompass the itemslisted thereafter and equivalents thereof as well as additional items.References to “or” may be construed as inclusive so that any termsdescribed using “or” may indicate any of a single, more than one, andall of the described terms. As used herein, the term “fastener” refersto any mechanical device that joins or secures two or more objectstogether and is not limited to the particular style of fastenersdisclosed or illustrated herein.

The present disclosure is directed to a fastener associated with an RFIDtag including a semiconductor chip. The semiconductor chip is incommunicative connection with the fastener, and at least part of theRFID tag can be embedded within or otherwise attached to the fastener,including on a surface thereof. In some embodiments the antenna that istraditionally part of an RFID tag is eliminated and, instead, thefastener itself acts as the antenna. When acting as an antenna, thefastener transmits modulated RF signals from the RFID semiconductor chipto an external receiver, as would be known of those to skill in the art.

In accordance with one embodiment of the present disclosure, anindividual RFID tag with an integrated circuit in the form of asemiconductor chip is attached, i.e. secured to a fastener. The RFID tagcan be attached to the fastener at any location, such as on the head oron the shaft of the fastener, as shown in one example embodiment inFIGS. 3A-3C. For example, as shown in FIG. 3A, the RFID tag 12 has acircuit/chip 26 embedded in the head 18 of fastener 10, such that thetag 12 is generally flush with the surface of the head 18. In thisembodiment the chip 26 is also embedded in the shaft 14 toward thedistal end 22 of the shaft, as shown in FIGS. 3B and 3C, such that thetag is generally flush with the surface 24 of the distal end 22, anddoes not extend past the distal most end of the threads 28. An exemplaryembodiment of the chip is further shown in the schematic of FIG. 4 ,where the chip 26 is separate from the fastener 10, but in communicativeconnection via one or more wires 30 or connection pins (not shown) tothe fastener, which is acting as the antenna.

Fastener 10 can be any of a variety of different types of fasteners. Inthe present exemplary embodiments, fastener 10 is a screw that is shapedand sized in accordance with its intended use. Examples of other typesof fasteners and their components include, but are not limited to,nails, bolts, rivets, screws, studs, nuts and washers. As shown in FIG.3B, Fastener 10 has an elongate body or shaft 14 including a proximalend 16 and a distal end 22, opposite the proximal end 16, and a head 18supported at the proximal end 16 of the shaft 14. The elongate body 14may be threaded on an outer surface thereof, such as with a screw, orcan be smooth, such as with a nail, and can engage with other fastenercomponents such as a washer, nut, sleeve, or other components, as wouldbe known to those of skill in the art. In this embodiment, as can beseen from FIGS. 3A-3C, the head 18 has a diameter that is larger thanthe diameter of the shaft 14.

The semiconductor chip 26 can be of a conventional construction and canbe obtained from any of a variety of manufacturers, including thoselisted at http://www.rfidtags.com/manufacturer-directory. The particularspecification of the chip can be chosen based upon the particularapplication, as would be known to those of skill in the art. One exampleof a suitable commercially available chip is a Higgs 4 chip availablefrom Alien, the specifications of which are provided in FIG. 12 or thecurrent chip versions with updated specifications. Depending upon theapplication the chip 10 may be passive, active, or semi-active.Likewise, depending upon the application the chip 10 may operate in anyof the three frequency ranges in which RFID systems typically operate,namely: 30-400 kHz (low frequency), 3-30 MHz (high frequency) and 300MHz-1 GHz (ultra-high frequency). In one exemplary embodiment, the chipis a passive chip that operates in ultra-high frequencies. For example,but not limitation, the chip can be a passive chip that operates inapproximately the 860-960 MHz range.

The dimensions of the chip 26 can likewise vary depending upon theapplication. For example, but not limitation, the chip can have a widththat is less than about 1.5 cm, including 0.0 cm. The chip can also havea length that is less than about 1.5 cm, or any other length between 0.0cm and 1.5 cm. In certain embodiments, the width and length of the chipis determined such that the entire chip fits on or within the desiredmounting location of the fastener without extending past the surface ofthe fastener.

The chip 26 is loaded to contain information about fastener 10 that canbe easily read by an electronic device and displayed, as isconventional. Chip 26 may include information related to fastener 10such as the manufacturing information, for example the partmanufacturer, serial number, product part number, lot history, recall orother historical information, instructions for use, or other informationthat can be displayed to an operator. The chip 26 may also includeinformation regarding the status or performance of the fastener 10, suchas whether the fastener has become loose or is no longer in place, ifdesired. The chip 26 can also be in communicative connection with one ormore sensors, such as, for example and not limitation, acoustic, sound,vibration, air flow, temperature, radiation, steam, stress, pressure,torque, displacement, chemical, pH, electromagnetic and/or ultrasonicwave, and current sensors, and/or any other type of sensor, as desired.The information from chip 26 of the RFID tag can also be easily added toan electronic record. Accordingly, RFID chip 26 can assist in trackingduring manufacturing and after installation of the fastener, improvingtraceability of the fastener, providing information about the fastener,assisting in the determination of the need for maintenance, adjustmentor replacement of the fastener, and assisting in the monitoring of theenvironment in which the fastener is located in a convenient andreliable manner.

The microchip 26 is integrated into any of a variety of conventionalfastener designs using current manufacturing techniques, such as bycounterboring a hole 20 within the head 18 and/or shaft 14 of thefastener 10, or by securing the microchip to the surface of the head 18and/or shaft 14 of the fastener 10. The embedded RFID chip does notinterfere with the operation of the fastener 10 because the fastenerstill operates and functions in the same manner with or without theembedded microchip 26.

The microchip 26 may be attached to the metal fastener using any methodknown in the art. For example, in an example embodiment, the RFID chip26 may be welded/soldered to the nut, bolt, and/or fastener. In anotherexample embodiment, the RFID chip 26 may be attached using, for example,industrial adhesives.

Utilizing the RFID chip 26 with the fastener 10 as the antenna toproduce an RFID tag provides a reliable solution, for traceability,anti-counterfeiting, sorting, post-disaster identification purposes,inventory control, maintenance, or anti-theft, particular in industriessuch as the aerospace and automotive industry where recalls andpost-disaster identification purposes can be time-consuming withconventional methods. The fastener 10 operating as the antenna alsosolves issues in the prior art concerning interference caused by themetal of the fastener, and provides a new and reliable solution to fortraceability, sorting, inventory control, etc. as enumerated above.

The ability of the fastener 10 to function as an antenna can depend upona number of factors. Some of these factors include, but are not limitedto, the conductivity of the material, an electrical connection to thefastener, and what is known as the “skin effect”—the tendency of currentfrom the generated RF to travel on the outer layer of conductivematerial.

The fastener 10 may be fabricated entirely, or in part, out of anelectrically conductive metallic material, in order to reduce the lossof RF energy as the current travels to the chip 26. In certainembodiments, the entire fastener 10 is fabricated out of an electricallyconductive metallic material. In other embodiments, only a portion ofthe fastener 10 is fabricated out of an electrically conductivematerial. For example, but not limitation, in one embodiment, only anouter layer of the fastener 10 is fabricated out of an electricallyconductive material.

The electrically conductive material in one embodiment can have aresistance less than about 5 ohms. In one embodiment, the electricallyconductive material has a resistance less than about 1 ohm. Examples ofelectrically conductive material include, but are not limited to,titanium, A-286, nickel-chromium alloys, such as Inconel™, other superalloys, stainless steel, alloy steel, aluminum, zinc-coated steel,titanium nitride-coated titanium, and naval brass, to name but a few,and may be fabricated in a facility that is certified to QualityStandards AS9100 and ISO9001, or the current versions of thesestandards. For example, but not limitation, in one embodiment, thefastener material is zinc-coated steel.

In addition to the above, the width (e.g. diameter) and length of thefastener 10 also affects the fastener's ability to function as anantenna. In one embodiment, for example, but not limitation, theapproximate length of the fastener can be determined by one of ordinaryskill in the art, based on the desired frequency range and the desiredradius of the fastener using the following three equations as they applyto cylindrical monopole antenna models:

$\begin{matrix}{{Length} = {{.24}\;\lambda*\frac{l/a}{1 + {l/a}}}} & {{Equation}\mspace{20mu}(1)} \\{l = {{\lambda/4} = {{c/4}f_{c}}}} & {{Equation}\mspace{14mu}(2)} \\{{Length} = {{.24}\frac{c}{fc}*\frac{{c/4}{afc}}{1 + {{c/4}{afc}}}}} & {{Equation}\mspace{14mu}(3)}\end{matrix}$

Equation 1 gives the ideal length given a known desired centerfrequency, where l is the length of a monopole with a theoretical radiusof zero that is determined by Equation 2, and a is the radius of themonopole cylinder. Combining Equations 1 and 2 yields Equation 3, whichcan help predict the length of the fastener given the desired centerfrequency, fc, and the desired radius. The constant c is the speed oflight, 300,000,000 m/s.

For example, if the desired frequency range was determined to be 902-928MHz and the desired radius of the screw was 5 mm, using Equations 1-3,and the range of optimal lengths would be from 7.31-7.52 cm.

The fastener 10 may be suited for use by any type of customer, includingend-users, commercial, and government customers. The customers can spanany number of industries/fields, such as, but not limited to, themilitary (for example, military airframe manufacturing) aerospace (forexample, commercial airframe manufacturing, and aerospace propulsionmanufacturing), automotive, railway, maritime, medical, sports,nano-technology, computer, and construction industries/fields. In oneembodiment, the fasteners are for use in the aerospace industry, such asfor airframes, including fixed or rotary wings, or spacecrafts,including transport structures, satellites, and off-Earth habitats.

In certain embodiments, an impedance-matching device, or matchingnetwork, can be used to optimize the power transfer between the chip 26and the antenna. Any one or combination of transformers, resistors,inductors, capacitors, and transmission lines can be used. In oneembodiment, the matching network is an inductor, which can be, but isnot limited to, the use of a wire connected at either end to the chip 26and the fastener 10, such that it forms a loop. An exemplary circuitrepresentation 500 of the three components—the chip 510, theantenna/fastener 520 and the matching network 530—can be seen in FIG. 5.

An external reader is configured to read and retrieve the electronicinformation stored by the semiconductor chip 26. The semiconductor chip26 may be passively powered, such that the metal fastener 10 performingas the antenna receives RF energy from the external reader to permit theRFID integrated circuit 26 to be powered without a physical connectionto a power supply. Thus, the RFID tag is highly integrated and compactenough to function within the confines of the dimensions of thefastener. This provides a cost-effective alternative to a traditionalRFID tag and antenna. For example, the RFID tag may be integrated duringthe manufacturing of the nut, bolt, and/or fastener and may also besealed with a protective substance to further protect the RFID tag. Inthis embodiment, the metal interference and signal reflection of thefastener is used for longer read range of the RFID tag.

With respect to the RFID reader, any reader that is capable of obtaininginformation using radio waves from the RFID tag is suitable, andoptionally communicating the information contained in the tag tosoftware. RFID readers are usually associated with a range from whichthe tag can be read. Most readers typically have ranges that fallsomewhere between about one to about one hundred meters. Similar to RFIDtags, readers have antennas. The two most common types of antennas arelinear-polarized or circular polarized. The antennas used in the readerdepend on the read range of the tags, e.g. NFC or FFC. RFID readers canbe, but are not limited to, wireless, fixed, handheld, and/or USBpowered. Examples of commercial RFID reader manufacturers include, butare not limited to, Alien, Avery Dennison, Confidex, Fujitsu, Geoforce,Harting, HID Global, Indentix, Impinj, Invengo, Kathrein, Keonn, LairdTechnologies, MTI Wireless Edge, Omni-ID, RFMAX, SATO, Seeonic, SLS,SMARTTRAC, Tageos, ThingMagic, Times-7, TransCore, TSL, Turck, Vulcan,Xerafy, Zebra. An example of a reader capable of reading distances up tobetween 9 m and 15 m, depending on the tag, is the Alien ALR-H450Handheld RFID reader, for which the specifications are provided in FIG.11 , or RFID reader version with updated specifications.

In another embodiment, due to the metallic properties of the fastener,an antenna 28 may be included as part of the RFID tag. The antenna 28may be, for example, a patch antenna or an inverted-F antenna.Inverted-F antennas can be designed in multiple shapes and designs. Inthis embodiment, the patch antenna associated with the RFID tag isreduced in size so as not to modify the dimensions of the nut, bolt,and/or fastener beyond tolerance levels.

In another example embodiment, the physical size of the antenna may bereduced by adding meandering sections to an ordinary dipole antenna.Text, in the form of brand names and/or logos may also be used as ameandered line antenna. The reduced size of the antenna and/or RFID tagmay also reduce manufacturing costs of the RFID tag. In another exampleembodiment, certain dimensions of the fastener may be modified toaccommodate the dimension of the RFID tag, however that the finaldimensions of the fastener should remain the same.

In an example embodiment, the fasteners are tested mechanically fordurability, repeatability, and/or robustness (for example, accessibilityof the data, amount of data storage, etc.).

The following are examples of prototype testing, and should not beconstrued as limiting.

EXAMPLES Example 1—Characterizing the Antenna Behavior of a Fastener

In this example, a zinc-coated steel screw having a diameter of 0.9 cmand a length of 8.0 cm was used as the RFID antenna. In order tocharacterize the antenna behavior of the screw at the desired UHF rangeof 860-960 MHz, the reflection coefficient of the screw was determined.The reflection coefficient is the measure of how much of anelectromagnetic wave is deflected due to impedance mismatches. The pointalong the frequency spectrum where the reflection coefficient of anantenna reaches a minimum represents the point where the compleximpedance of the antenna is at zero, or is resonant. At this frequency,the power transmitted to the antenna is maximized and signals are bestintercepted. Essentially, an antenna acts as a narrow band-pass filter,where the center frequency is determined by the location of the minimumof the reflection coefficient.

To determine the frequency dependent reflection coefficient for thescrew, a Vector Network Analyzer (VNA) was used. A VNA is a two-portanalysis tool capable of determining the reflection coefficient to ahigh degree of accuracy along a frequency spectrum. In operation, itsends test signals through a port and then analyzes the returned signalsthrough a different port to determine the reflection coefficient,notated S₁₁, of the device under test (DUT), through which the signalstravelled.

Typically, antennas are attached to the VNA for testing using aSubMiniature version A (SMA) connector. In order to characterize thescrew antennas, a connector was fashioned to attach them to a male SMAconnector. This connector consisted of a female SMA on one side and amale banana plug on the end. In order to test each screw, a hole thesize of a banana plug was drilled into them. The SMA-banana transformerwas then used to connect the screws to the VNA.

In order to get the best results from the VNA, for each round of testingthe VNA was calibrated using an automatic electronic calibrator (eCal)that was attached to the VNA using semi-rigid SMA cables. When testingthe screw-antennas, the semi-rigid SMA cables were kept in the exactlocation they resided during calibration. Additionally, the S₁₁ data ofthe SMA-banana connector was saved for each round of testing andsubsequently subtracted from the antenna S₁₁ data, in order to removeits effect from the data.

The S₁₁ data for various screw-antennas was saved from the VNA and thefrequency data was separated from the S₁₁ data. Next the same series ofsteps was applied to data from the SMA-banana connector, keeping onlythe S₁₁ data, not the superfluous frequency data. Finally, to get themost accurate S₁₁ data for the antennas, the S₁₁ of the SMA-bananaconnector was subtracted from each data point along the frequencyspectrum.

In short, the above-described testing process is set forth below in thefollowing steps:

-   -   1. Drill a ⅛ inch diameter hole in the screw 1 cm deep    -   2. Calibrate VNA using semi-rigid SMA cables and an eCal    -   3. Sand the inside of the hole before using the SMA-Banana        connector to attach the screw to port 1 of the VNA    -   4. Take S₁₁ data across the 860-960 MHz frequency spectrum and        save the information in a .prn file    -   5. Use the S₁₁ data the minimum point in Equation 4 to find the        real impedance, i.e. the resistance

$\begin{matrix}{R_{L} = {Z_{o}\frac{1 + \Gamma_{\min}}{1 - \Gamma_{\min}}}} & (4)\end{matrix}$

-   -   6. Use two points along the S₁₁ graph and Equation 6 to        determine the values of the inductor and capacitor    -   7. Construct a circuit as shown in FIG. 3

The S₁₁ data collected for each antenna was then compared to thetheoretical S₁₁ data calculated using the MATLAB Antenna Toolboxdeveloped by MathWorks of Natick, Mass. FIG. 6 illustrates exemplarycode for theoretical reflection coefficient data calculated using theMATLAB Antenna Toolbox for comparison with an RFID fastener. For thisprocess, first a cylindrical monopole antenna model for the screw wasconstructed in MATLAB. Next, the impedance of the model antenna wasanalyzed. Wherever the complex impedance was zero along the frequencyspectrum, the real impedance at that frequency was recorded as thetheoretical “load” impedance of the antenna. Next when analyzing the S₁₁of the model antenna, the value of the load impedance previouslyrecorded was included. Using this series of steps, the bestapproximation of the S₁₁ of the theoretical cylindrical monopole modelof the antenna was found.

In order to obtain a circuit representation of the screw, the reflectioncoefficient data, S₁₁ data, was converted into impedance data along thefrequency spectrum.

The first step for this process is determining the real impedance of thescrew, which consequently should theoretically match the “load”impedance determined by MATLAB. The antenna has a purely real impedanceat the frequency where S₁₁ is at an absolute minimum; the point can beseen in FIG. 7 around 840 MHz.

The load impedance, ZL, of the screw was calculated using Equation 5 (byusing the reflection coefficient equation) and Equation 6, with theknowledge that the VNA had an impedance of 50 ohms (Zo) the loadimpedance (ZL), after converting the reflection coefficient fromDecibels.Γ=

10

{circumflex over ( )}(Γ_dB/20)=

10

{circumflex over ( )}(S_11/20)  (5)Γ=(Z_L−Z_o)/(Z_L+Z_o)  (6)

Next, two points along the S₁₁ curve were chosen near either side of theresonance frequency, approximately 840 MHz, shown in FIG. 7 .Rearranging the reflection coefficient equation, along with the fullimpedance equation, Equation 7, yields Equation 8.Z_L=R_L+

jX

_L  (7)Abs

(R

_L+

jX

_L)=Z_o(1+Γ)/(1−Γ)  (8)

Taking Equation 8 and substituting the impedance, with the impedance ofa capacitor, inductor and the previously calculated real antennaresistance in series, Equation 9, ultimately leads to Equation 10.R_L+jX_L=R_a+jωL_a+1/jωC  (9)ωL−1/ωC=√(

Z_o

{circumflex over ( )}2((1+Γ)/(1−Γ)){circumflex over ( )}2−

R_a

{circumflex over ( )}2)  (10)

By using the antenna load impedance, the impedance of the VNA, and theS11 value at two frequencies, approximations of the inductor value andcapacitor value emerge. Because Equation 10 includes two variables, Land C, two points along the S11 curve are required in order to constructa system of equations to solve for both. When analyzing the point to theleft of the resonance frequency the product of the square root (leftside of Equation 10) will be negative, and when analyzing the point tothe right of the resonance frequency the product of the square root willbe positive—this is due to the nature of capacitive and inductiveeffects around the resonance frequency.

In short, the process for modeling the screw as a cylindrical monopoleantenna is set forth in the steps below:

-   -   1. Using MATLAB code, replace the length and width with the        appropriate values for the screw.    -   2. Suppress the S₁₁ section and find the impedance, record the        value of the real impedance at the frequency where the reactance        is zero.    -   3. Use this recorded value as the load impedance, “load” in the        code, and calculate the S₁₁ data.    -   4. Repeat steps 5-7 from the last section to convert the S₁₁        data into a circuit model.

The reflection coefficient data obtained using the VNA and thetheoretical model match almost perfectly, as shown in FIGS. 13A and B,respectively, proving that the modeling of a screw as a cylindricalmonopole can be an accurate model of the electromagnetic behavior of thescrew.

Example 2—Constructing a Matching Network

In order to optimize the power transfer between the RFID chip and thetag antenna (i.e. the screw), a matching network was constructed. Inorder to determine an optimal inductor value to be used for a matchingnetwork, a tunable inductor was placed in the circuit and the value ofthe inductor was adjusted to maximize the optimal distance of operation.

Initially, a circuit with a T-matching networks, as shown in FIG. 8 ,was constructed by designing the printed circuit board (PCB) shown inFIG. 9 and attaching the necessary components. Although this PCB wasoriginally designed for a T-matching network, it was determined that asingle inductor could be a more cost-effective option. Accordingly, thetesting PCB was constructed in such a way to fit the circuit design inFIG. 5 instead. The RFID chip was soldered to the PCB, a pin wassoldered into the via hole and then soldered into the screw and finallya wire was soldered on either end of the RF signal connector of the RFIDchip and the via hole attached to the screw, thus creating the circuitdescribed by FIG. 5 . The wire was then twisted gently to create acircular loop in the center, acting as a loop inductor, to construct atransponder.

Next the RFID reader, the ALR-H450 by Alien, was placed perpendicularwith the transponder. The wire was twisted tighter and looser tomodulate the inductance while the Geiger function of reader was usedsimultaneously to discover the maximum distance away from the screw thata consistent, even faint, signal was picked up. For the variousinductances the diameter of the loop was recorded along with the maximumdistance of minimum communication. The diameter of the loop was thenconverted into inductance using Equation 11, where D is the diameter ofthe loop, d is the diameter of the wire, and μ_r is the relativepermeability of the wire.L_loop=μ_oμ_r(D/2)(ln(8D/d)−2)  (11)

A scatter plot of the loop diameter vs. maximum distance of minimumcommunication data for a screw having a diameter of 0.9 cm and a lengthof 7.6 cm is shown in FIG. 10 . It can be seen from FIG. 10 that at itspeak performance, this screw can be used as an RFID antenna at upwardsof 0.5 m away.

In summary, the process for finding an optimal inductance of a matchingnetwork is set forth in the steps below:

-   -   1. Develop a PCB similar to the one shown in FIG. 9 , except        with only space for the bottom right component, i.e. nothing        connected to the top port of the RFID chip    -   2. Drill a hole in the screw large enough for a pin    -   3. Solder the Alien RFID chip to the PCB, solder a pin through        the via into the screw    -   4. Attach a wire between the RFID chip and the via hole,        twisting the wire to form a loop    -   5. Set the ALR-H450 reader to Geiger mode    -   6. Record the diameter of the wire loop    -   7. Set the screw upright and aim the reader perpendicularly at        it, as shown in FIG. 9    -   8. Move the reader toward the screw, holding the trigger button,        until the Geiger counter beeps    -   9. Record the distance from the screw that the reader first read        the RFID chip    -   10. Twist the loop wire to a new diameter    -   11. Repeat steps 6-10 until a loop diameter has been found that        maximizes the distance at which the RFID chip can be read    -   12. Convert this diameter into an inductance using Equation 11

Example 3—Working Prototype

A first working prototype, as shown in FIG. 14 , was constructed using a0.9 cm zinc-coated steel screw. A PCB was soldered to the screw, and aT-matching-network was also used. However, it was determined that azinc-coated screw having a diameter of 0.7 cm and the use of a tunableinductor matching network, as described above, provided the best workingprototype. The working prototype was capable of consistent communicationwith the ALR-H450 reader at approximately 0.5 m.

While various embodiments of the invention have been particularly shownand described, it will be understood by those skilled in the art thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the invention. For example, thematerials disclosed herein may be readily changed, as may the dimensionsand geometric configurations. The fastener itself may have a differentconfiguration other than that which is illustrated, and the microchipmay be secured to the surface of, or embedded within the head, or theshaft, or both the head and shaft of the fastener. Also elements thatare shown in combination may be shown in different combinations or maybe eliminated. Elements shown as unitary (or a singular piece) may alsobe composed of more than one piece, and those composed of more than onepiece may be made unitary. Thus, the details of these components as setforth in the above-described examples, should not limit the scope of theclaims.

Those skilled in the art will appreciate that the conception, upon whichthis disclosure is based, may readily be utilized as a basis fordesigning other products without departing from the spirit and scope ofthe invention as defined by the appended claims. Therefore, the claimsare not to be limited to the specific examples depicted herein. Forexample, the features of one example disclosed above can be used withthe features of another example. Furthermore, various modifications andrearrangements of the parts may be made without departing from thespirit and scope of the underlying inventive concept. For example, thegeometric configurations disclosed herein may be altered depending uponthe application, as may the material selection for the components. Thus,the details of these components as set forth in the above-describedexamples, should not limit the scope of the claims.

Further, the purpose of the Abstract is to enable the U.S. Patent andTrademark Office, and the public generally, and especially thescientists, engineers and practitioners in the art who are not familiarwith patent or legal terms or phraseology, to determine quickly from acursory inspection the nature and essence of the technical disclosure ofthe application. The Abstract is neither intended to define the claimsof the application nor is intended to be limiting on the claims in anyway.

What is claimed is:
 1. An RFID fastener comprising: a semiconductorchip; an antenna comprising a metal fastener having a proximal end and adistal end and configured to secure two or more objects together; andwherein the semiconductor chip is in communicative connection with theantenna such that the RFID fastener transmits modulated RF signals fromthe semiconductor chip to an external reader during use.
 2. The RFIDfastener of claim 1, wherein the semiconductor chip is a passive chipand receives RF energy from the external reader that powers thesemiconductor chip without physical connection to a power supply.
 3. TheRFID fastener of claim 2, wherein the semiconductor chip operates inultra-high frequencies at approximately the 300 MHz-1 GHz range.
 4. TheRFID fastener of claim 2, wherein the semiconductor chip operates inhigh frequencies at approximately the 3-30 MHz range.
 5. The RFIDfastener of claim 2, wherein the semiconductor chip operates in lowfrequencies at approximately the 30-400 kHz range.
 6. The RFID fastenerof claim 1, wherein the semiconductor chip is in communicativeconnection with one or more sensors, the one or more sensors selectedfrom a group consisting of acoustic, sound, vibration, air flow,temperature, radiation, steam, stress, pressure, torque, displacement,chemical, pH, electromagnetic, and ultrasonic wave sensors.
 7. The RFIDfastener of claim 1, wherein the semiconductor chip is separate from themetal fastener and is connected to the metal fastener by one or moreconnectors that provide the communicative connection between thesemiconductor chip and the metal fastener.
 8. The RFID fastener of claim1, wherein the metal fastener comprises: a head comprising a firstdiameter and a top surface and a side surface; an elongate bodyextending from the head including an outer surface that is either smoothor threaded; and wherein the semiconductor chip fits on or within adesired mounting location of the metal fastener without extending beyonddimensions of the top surface, side surface or outer surface of themetal fastener.
 9. The RFID fastener of claim 8, wherein the desiredmounting location is the head of the metal fastener, and thesemiconductor chip is supported within a recess in the head of the metalfastener so that the semiconductor chip is generally flush with the topsurface of the head.
 10. The RFID fastener of claim 8, wherein thedesired mounting location is a shaft of the metal fastener.
 11. The RFIDfastener of claim 10, wherein the semiconductor chip is supported in arecess within the distal end of the shaft, such that the semiconductorchip does not extend beyond a bottom surface of the shaft.
 12. The RFIDfastener of claim 8, wherein the semiconductor chip is sealed with aprotective sub stance.
 13. The RFID fastener of claim 1, wherein themetal fastener comprises electrically conductive material disposed atleast on an outer layer of the metal fastener, the electricallyconductive material having a resistance less than about 5 ohms.
 14. TheRFID fastener of claim 13, wherein the electrically conductive materialis selected from a group including titanium, A-286, nickel-chromiumalloys, super alloys, stainless steel, alloy steel, aluminum,zinc-coated steel, titanium nitride-coated titanium, and naval brass.15. The RFID fastener of claim 1, wherein the semiconductor chip storesinformation related to the metal fastener.
 16. The RFID fastener ofclaim 15, wherein the information is selected from a group consisting ofstatus of the metal fastener, performance of the metal fastener,identifying information, manufacturing information, recall history, andinstructions for use.
 17. The RFID fastener of claim 15, wherein theinformation is displayed to an operator and stored in an electronicrecord.
 18. The RFID fastener of claim 1, wherein the antenna is ameandered line antenna.
 19. The RFID fastener of claim 1, furthercomprising an impedance-matching device constructed and arranged tooptimize a power transfer between the semiconductor chip and theantenna.
 20. The RFID fastener of claim 19, wherein theimpedance-matching device is selected from a group consisting oftransformers, resistors, inductors, capacitors, and transmission lines.